On Mon, 17 Nov 2025 12:44:58 +0000 Steven Price <[email protected]> wrote:
> On 13/11/2025 10:39, Boris Brezillon wrote: > > The meat in lock_region() is about packing a region range into a > > single u64. The rest is just a regular reg write plus a > > as_send_cmd_and_wait() call that can easily be inlined in > > mmu_hw_do_operation_locked(). > > > > v2: > > - New patch > > > > Signed-off-by: Boris Brezillon <[email protected]> > > --- > > drivers/gpu/drm/panthor/panthor_mmu.c | 14 +++++--------- > > 1 file changed, 5 insertions(+), 9 deletions(-) > > > > diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c > > b/drivers/gpu/drm/panthor/panthor_mmu.c > > index 186048fc2c25..f109c1588186 100644 > > --- a/drivers/gpu/drm/panthor/panthor_mmu.c > > +++ b/drivers/gpu/drm/panthor/panthor_mmu.c > > @@ -538,11 +538,9 @@ static int as_send_cmd_and_wait(struct panthor_device > > *ptdev, u32 as_nr, u32 cmd > > return status; > > } > > > > -static int lock_region(struct panthor_device *ptdev, u32 as_nr, > > - u64 region_start, u64 size) > > +static u64 pack_region_range(u64 region_start, u64 size) > > { > > u8 region_width; > > - u64 region; > > u64 region_end = region_start + size; > > > > if (!size) > Extra context: > > return 0; > Rather than skipping the lock for size==0 you are now performing a lock > with LOCKADDR=0. The best documentation I can find for that says (for > LOCKADDR_SIZE in the Midgard architecture): "Values in the range 0 to 10 > are undefined and should not be used". > > I think later versions upped the minimum to 14 (log2(1<<15)-1) for > reasons due to supporting larger page sizes. > > While I suspect this might work (since we don't actually need a lock > region when size==0) I don't think we should be relying on undefined > behaviour. > > I think the simple solution is to move the size==0 check up into the caller. Right. I addressed that in patch 4 (which basically removes mmu_hw_do_operation_locked()), but I can do it here too. > > Thanks, > Steve > > > @@ -565,11 +563,7 @@ static int lock_region(struct panthor_device *ptdev, > > u32 as_nr, > > */ > > region_start &= GENMASK_ULL(63, region_width); > > > > - region = region_width | region_start; > > - > > - /* Lock the region that needs to be updated */ > > - gpu_write64(ptdev, AS_LOCKADDR(as_nr), region); > > - return as_send_cmd_and_wait(ptdev, as_nr, AS_COMMAND_LOCK); > > + return region_width | region_start; > > } > > > > static int mmu_hw_do_operation_locked(struct panthor_device *ptdev, int > > as_nr, > > @@ -602,7 +596,9 @@ static int mmu_hw_do_operation_locked(struct > > panthor_device *ptdev, int as_nr, > > * power it up > > */ > > > > - ret = lock_region(ptdev, as_nr, iova, size); > > + /* Lock the region that needs to be updated */ > > + gpu_write64(ptdev, AS_LOCKADDR(as_nr), pack_region_range(iova, size)); > > + ret = as_send_cmd_and_wait(ptdev, as_nr, AS_COMMAND_LOCK); > > if (ret) > > return ret; > > >
